1. Technical Field
This invention relates to a supply circuit supplying electric current to a Hall sensor multiplication circuit in such a way that the absolute value of the output voltage of the multiplication circuit is changed for about 0.01% at most when the polarity of this output voltage is reversed.
2. Description of the Prior Art
In known watthour meters or wattmeters which are based on the Hall effect a multiplication circuit reversing the polarity of the output Hall voltage is used to compensate internal disturbances of the meter. Such meters are described e.g. in DE 37 11 978 A1 and DE 37 02 344 A1.
A known multiplication circuit is composed of a Hall sensor 6' whose first voltage terminal is connected to the inverting input of an operational amplifier A', the second terminal, however, is connected to the output of the multiplication circuit, and of a switching bridge which is made of controlled switches 2',3',4',5' and which supplies electric current across a resistor 7' being connected to one terminal of a load to current terminals of the Hall sensor 6' (FIG. 1). A signal P from a voltage to frequency converter controls the polarity of the Hall voltage U.sub.H at the multiplication circuit output by exchanging the current terminals of the Hall sensor 6'. The described multiplication circuit performd in a monolithic technology provides good results when the Hall sensor is performed separatedly from the rest of the multiplication circuit. When, however, the Hall sensor is integrated with the rest of the multiplication circuit on a common substrate the accuracy of the polarity reversal of the Hall voltage U.sub.H is affected by the nonideally symmetric shape of the Hall sensor as well as by the nonlinearity originating from a barrier layer separating the Hall sensor from the substrate.